Three-dimensional ultrastructure of taste bud cells and nerve fibers in the mouse.

Abstract

The three-dimensional ultrastructures of the taste bud cells and the nerve fibers in the mouse were investigated by means of electron microscopy using serial ultra-thin sections.Most of the taste bud cells were spindle-shaped and smooth in outline, but a few of type-II cells protruded in cytoplasmic processes from the basal portions. The nerve fibers entering the taste buds through the basal lamina, branched several times, the terminals were formed repeatedly, and then, they narrowed and back to slender, finally ending in the form of a teminal. The number of nerve fibers and terminals which innervate a single taste bud cell differed among the cell types. Each type of cell came in contact with the following per cell, type- I and basal cells with 1-2 nerve fibers, type- II cells with 1-4 nerve fibers, and type-DI (gustatory) cells with 2-4 nerve fibers. The number of nerve terminals in contact with each type of cell was 1-2 per cell in type- I and basal cells, 2-4 type-il and 3-6 in type-III. The nerve fibers which came in contact with type-III cells always formed several (mean number of 8 per cell) afferent synapses. A single nerve fiber innervated 4-14 (mean number of 9) taste bud cells which were composed of different cell types. Seven of nine nerve fibers innervated both type-DI cells and other types of cells. This uggests that most of the nerve fibers in the taste bud not only transmit gustatory stimulus but also have other functions, such as the trophic effect on the taste bud cells.